1. Field of the Invention
The present invention relates to integrated circuit technology. More particularly, the present invention relates to an integrated circuit system including mating sets of face-to-face integrated circuit dice.
2. The Prior Art
As process geometries scale, the portion of the area of digital-logic function integrated circuits such as field-programmable-gate-array (FPGA) integrated circuits and mixed digital and analog function integrated circuits that must be devoted to input/output circuits (I/O) represents an increasing percentage of the die area relative to logic gates. A secondary cost issue is that often customers may need a significant amount of I/O and not many gates. Presently, such customers end up paying for un-needed gates in order to obtain needed I/O. The reverse is true as well. This represents an opportunity to deliver a more cost-effective product to customers.
Another problem is that some manufacturers envision creating a number of system-on-a-chip (SOC) integrated circuits and derivatives that employ FPGA and other programmable logic technology. These derivatives will have varying quantities and functions of analog peripherals depending on application. Many variations of analog peripherals are envisioned. In addition, the number of FPGA gates needed for each set of peripherals will be customer dependent, again creating a situation where the customer is paying for un-needed gates.
The industry has not come up with a good solution for the I/O problem to date. The current trend is to offer several variations of products with different combinations of I/O structures and gate counts. For example, some I/Os are constructed as in-line circuits, while others are staggered. Some I/Os may include different features such as LVDS or PCI-compliant circuits or circuits used to implement other standards. Some higher density I/O circuits require that electro-static discharge (ESD) protection circuits be reduced or eliminated to allow more space on the chip for more I/O circuits. Therefore, with prior art systems, there is often a trade-off between ESD protection and the number of available I/O circuits. Another solution is to use so-called I/O immersion where I/Os can be programmed anywhere in the FPGA fabric, thereby decoupling the number of I/Os from the number of gates, because the I/O circuits are not limited to the perimeter of the device. This solution however requires flip-chip packaging. Flip-chip packaging is the art of bonding pads distributed anywhere on the face of an IC directly to a package without use of wires. Flip-chip packaging, presently and in the reasonably-foreseeable future, will still add enough cost to the product to offset any cost savings realized from the solution.
The industry in general is looking at a number of so-called 3-D packaging variations. None of these variations are employing 3D packaging to solve the above-described I/O problem.